Conventionally, lithium secondary batteries (typically, lithium-ion batteries) have been utilized as high-performance secondary batteries. A lithium secondary battery comprises a positive electrode including a positive electrode active material made of a lithium-containing complex oxide, a negative electrode including a negative electrode active material capable of storing and releasing lithium ions, a separator interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte that impregnates the positive electrode, the negative electrode, and the separator. When manufacturing the lithium secondary battery, the positive electrode, the negative electrode, and the separator are assembled and impregnated with the nonaqueous electrolyte, and charging is subsequently performed.
When the lithium secondary battery is being manufactured, a metallic foreign substance (contaminant) such as iron (Fe) or copper (Cu) may be conceivably mixed in from the outside. When such a metallic foreign substance is dissolved in the nonaqueous electrolyte during a charge and is deposited in a concentrated manner on the negative electrode, there is a risk that the deposit may break through the separator to reach the positive electrode and cause a short-circuit. In consideration thereof, conventionally, various techniques have been proposed in order to prevent short-circuits attributable to metallic foreign substances.
Patent Literature 1 describes stabilizing battery characteristics by injecting an electrolytic solution into a battery, performing initial charge and discharge at an alternating current with a frequency of 1 Hz or higher and 1000 Hz or lower, and providing a standing time of 1 hour or more and 48 hours or less after the initial charge and discharge. With the technique disclosed in Patent Literature 1, by repetitively applying such an AC voltage, metal that is mixed in as a foreign substance on the positive electrode when the voltage rises is dissolved into the electrolytic solution. In addition, when the voltage drops, a negative electrode potential is held at or above a dissolution potential of the metal and metal ions are diffused within the electrolytic solution without being deposited on the negative electrode. By providing the standing time, ions created by the dissolution spread over a wide area, and even if the ions are deposited on a surface of the negative electrode, the ions are not concentrated at one location.
Patent Literature 2 describes performing a charge of 1 hour at least once, subsequently performing a discharge until potential of a negative electrode reaches 2.0 V or higher and 3.35 V or lower with respect to an oxidation-reduction potential of lithium, and providing a standing time of 3 minutes or more in this state.
Patent Literature 3 describes charging to 0.01% to 0.1% of a battery capacity for an initial charge and subsequently providing a standing time of 1 to 48 hours.